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BIOC40H3 (14)

Lecture 1

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Biological Sciences
Connie Soros

Plant Physiology – Lecture 1  Plant Physiology –isthediscipline ofbotanyconcernedwiththefunctioning, (orphysiology) ­ Relatedfieldsinclude plantmorphology, plant ecology, phytochemistry, cell biology, andmolecularbiology  Fundamental processessuchas photosynthesis, respiration, plant nutrition, plant hormonefunctions, tropisms, nasticmovements, photoperiodism, photomorphogenesis, circadianrhythms, environmental stressphysiology, seedgermination, dormancy andstomata functionandtranspiration, bothpartsofplant waterrelations, arestudiedby plant physiologists PLANTSAREAMAZING  Spectacular diversityofsize(1cm – 100+m)  Largediversityofmorphology(form andshape)  Plant physiologistsstudymodel organisms(Arabidposis –shortgenerationtimes and smallgenome+)  These modelsare usefulbecauseallplants, regardlessoftheir specific adaptations, carryout basicallythe sameprocesses andarebasedon the samearchitectural plan  We cansummarizethemajordesign elementsas: ­ AsEarth’sprimaryproducers, green plants aretheearth’sultimatesolar collectors, harvestingthesun’s energyandconvertinglight energytochemical energy, whichtheystoreinbonds formedwhenthey synthesize carbohydratesfrom carbondioxide andwater ­ Withtheexceptionofafew reproductivecells, plantsarenon-motile, asa substituteformotility, theyhave evolvedtheabilitytogrow towardessential resources, suchas light, waterandmineralnutrients throughout theirlifespan ­ Plants arestructurallyreinforcedto supporttheirmass astheygrowtowardsunlightagainst the pull ofgravity ­ Plants havemechanismsformoving waterandmineralsfromthesoiltothe sitesofphotosynthesisand growth, aswellasmechanisms formovingthe productsofphotosynthesistononphotosynthetic organs andtissues ­ Plantslosewatercontinuouslybyevaporation and haveevolvedmechanismsforavoidingdesiccation PLANT STRUCTURE  The vegetative plant body hasthree mainorgans: 1. Leaf –forphotosynthesis 2. Stem –forsupport 3. Root –anchorage and absorptionofwater andminerals  Leaves areattachedatthestem at nodes andtheregionbetweenthetwonodesiscalledtheinternode  The stemwithleavesiscalledtheshoot  The growingtipwithlocalizedregionsofongoingcelldivisioniscalledthe shoot apicalmeristem SAM *  The regions oftheshootapical meristemthatwillform leavesarecalled leaf primordia  Atthe axils ofleavesare axillarybuds withlateralmeristems (notmaingrowingtip) QUICKREVIEW –PLANTANATOMY 1. Leaves o Epidermis– the outermost layerof plant cells o Cuticle –multilayeredcoating(cutin, cutanandwaxes) thatcoversthe outer cellwallsofthe epidermis andrestrictspassageofwater andgassesinto and outof theplant o Mesophyll – photosyntheticcellsfoundinthegroundtissueof plants (palisade–foundjustundertheleafepidermis, thetop1-3layers ofpillar shaped photosynthetic cellswithlittle airspace betweenthem; spongy –usuallylocatedbeneaththepalisade, irregularshapedmesophyllcellssurroundedbylargeair spaces) o Stomate –(stoma, plural stomata)amicroscopic poreintheleaf epidermiswhichregulates gas exchange (water and CO2)ofleavesby controllingthepore opening. Thisisdonebya pair of guard cells attheopening o VascularTissue –plant tissuesspecializedforthetransportofwater(xylem)andphotosyntheticproducts(phloem)andaresurrounded byalayer ofcellscalledthebundlesheath 2. Stems o Epidermis– alsosurrounds thestem o Ground Tissue–pith, theinner-most portionofthestem, andthe cortex, theouter layerofgroundtissuetotheinsideoftheepidermis andtotheoutside ofthevascular cambium o VascularTissue –xylem, moveswater up ­ phloem movesphotosynthatesdown ­ separatingthexylem andphloemis the vascularcambium, alateralmeristem thatgivesrisetosecondary xylemand phloem elements 3. Roots o Taproot –themainsinglerootaxisfromwhichlateral rootsdevelop o RootApicalMeristem (RAM) –at thetip oftheroot, agroup ofcellsthat retainthecapacitytoproliferate andwhose ultimatefate remainsundetermined o RootCap –cells attheroot apexthat cover andprotectthemeristematiccellsfrom mechanicalinjuryastheroot movesthroughthe soil o Epidermis– surroundstheroot o Ground Tissue–cortex, theouter layeroftheroot delimited ontheoutsidebythe epidermis and onthe inside bythe endodermis, a specializedlayer of cellswitha Casparianstrip (a bandinthecellwallsthatisimpregnatedwiththewaxlike, hydrophobicsubstance suberin, that preventswater andsolutesfrom enteringthe xylem bymovingbetween the endodermal cells) surroundingthe vascular tissue o VascularTissue –xylem, moveswater up ­ phloem movesphotosyntheticproductsdown ­ vascular cambium betweenthexylem andphloem o Pericycle–meristematiccellsforming the outermost layer ofthe vascularcylinder, interiortotheendodermis, aninternalmeristematic tissuewhich givesrisetolateral roots o RootHairs –microscopicextensions ofroot epidermalcellsthat greatlyincreasethesurfaceareaofthe root, providinggreater capacity forabsorptionofsoilions and soilwater (toalesser extent)  Twocategoriesofseed plants
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